The U.S. Centers for Disease Control and Prevention calls it “one of the ten most important public health measures of the 20th Century.” A new vaccine? A cure for a major disease? No—the CDC is referring to the addition of fluoride to drinking water to prevent tooth decay.

Fluoride is a chemical compound found in foods, soil and water. Its presence in the latter, in fact, was key to the discovery of its dental benefits in the early 20th Century. A dentist in Colorado Springs, Colorado, whose natural water sources were abundant with fluoride, noticed his patients' teeth had unusual staining but no tooth decay. Curious, he did some detective work and found fluoride in drinking water to be the common denominator.

By mid-century, fluoride was generally recognized as a cavity fighter. But it also had its critics (still lively today) that believed it might also cause serious health problems. Ongoing studies, however, found that fluoride in tiny amounts—as small as a grain of sand in a gallon of water—had an immense effect strengthening enamel with scant risk to health.

The only condition found caused by excess fluoride is a form of tooth staining called fluorosis (like those in Colorado Springs). Fluorosis doesn't harm the teeth and is at worst a cosmetic problem. And it can be avoided by regulating the amount of ingested fluoride to just enough for effectively preventing tooth decay.

As researchers have continued to learn more about fluoride, we've fine-tuned what that amount should be. The U.S. Public Health Service (PHS), which sets standards for fluoride in drinking water, now recommends to utilities that fluoridate water to do so at a ratio of 0.7 mg of fluoride to 1 liter of water. This miniscule amount is even lower than previous recommendations.

The bottom line: Fluoride can have an immense impact on your family's dental health—and it doesn't take much. Excessive amounts, though, can lead to dental staining, so it's prudent to monitor your intake. That means speaking with your dentist about the prevalence of fluoride in your area (including your drinking water) and whether you need to take measures to reduce (or expand) your use of it.